Glow discharge tube



Feb. 3 1959 A. KOELEWIJN G'LOW DISC'HARGE TUBE Filed April 17, 1957 INVENTQR ARIE KOE.LE WIJN BYM AGENT United States Patent GLOW DISCHARGE TUBE Arie Koelewijn, Eindhoven, Netherlands, assignor to North American Philips Company, Inc., New York, N. Y., a corporation of Delaware Application April 17, 1957, Serial No. 653,388

Claims priority, application Netherlands April 28, 1956 3 Claims. (Cl. 313-198) The invention relates to a glowdischarge tube having only two electrodes in the primary discharge path.

Due to the heat produced by the main discharge in a gas tube, the density of gas in the vicinity of the main cathode will be decreased during operation, with a con comitant change in breakdown voltage. This change between the breakdown voltage of a cold gas tube and the different breakdown voltage of a hot tube produces erratic operation of circuits connected to the tube.

The primary object of the invention is to provide a gas discharge tube which has substantially the same breakdown voltage when it is hot as when it is cold.

The invention comprises a gas dscharge tube having a man cathode and anode between which the primary discharge takes place. In addition to the main discharge path electrodes are provided. or shaped, to establish a secondary discharge path somewhat removed from the main discharge path and at a location within the tube where the gas density does not vary appreciably between the cold and hot states of the tube. The electrodes defining the secondary discharge path are fixed relative to each other so that the breakdown voltage of the secondary discharge path is substantially the same when the tube is cold as the breakdown voltage of the main discharge path when the tube is hot. In this way, when the tube iscold, the intial breakdown occurs in the secondary discharge path and this breakdown is immediately transferred to the primary discharge path so that the electrodes which define the secondary discharge path do not heat up, and consequently, the density of the gas in the vcinity is not etlected by the brief secondary discharge.

The invention wiil be descrbed more fully with reference to the accompanying drawing in which:

Fig. 1 shows the variation of density of the gas in a glow discharge tube as a function of the dstance of the cathode from the bulb wall, and

Figs. 2 and 3 show a side view and aplan view of an electrode arrangement according to the invention.

In Fig. 1 the gas density d is plo'tted as a function of the distance a of the cathode from the wall of the bulb. In Fig. 1 the zero point on the abscissa indicates the cation of the cathode and the vertcal line on the right hand side of the figure indicates the bulb wall. Line I designates the density of the gas in the cold state of the tube and, as would be expected, shows that the density is uniform throughout the tube. Line 11 indicates the density variation when the tube is hot and particularly when the bulb is comparatively small. As may be seen, the density is lower in the immediate vicnity of the hot cathode than the uniform density of a cold tube, but, because the tube is a closed system with a constant number of gas molecules, the ara over curve II must be the same as the area over curve I, so the density near the wall of the bulb is higher for a hot tube than for a cold tube. At some point a (or locus of points) 2,872,608 Patented Feb. 3, 1959 between the wall and the hot cathode, the density of the gas is the same whether the tube is hot or cold, and it is at the point a that the secondary discharge path should be located.

In the embodiment of the invention shown in Figs. 2 and 3, the cathode 1 is in the form of a short trough having a U-shaped cross sction supported by a conductive rod 2. The main anode is the pointed end 3 of a wire 4 aimed directly at the open side of the cathode trough 1 with the point 3 in the same plane as the edges of the trough. A loop 5 is formed in the wire 4 in order to bring the wire into proxirnity with the supportng conductive rod 2. An auxiliary cathode 6 is provided adjacent a plate 7 to form an auxiliary discharge of about 1 a. so as to reduce ignition delay of the main discharge. The plate 7 also serves to shield the auxiliary discharge from the man discharge path. The members 1-7 are supported on contact pin studs extending through the wall of a tube envelope, or bulb, 8.

The secondary discharge path between the bottom end of loop 5 and the adjacent portion of rod 2 is located at a point within the bulb 8 which corresponds to the point a in Fig. 1. place between the loop 5 and the rod 2 before it takes place between anode 3 and the cathode 1 but is immediately shfted to the main discharge path between anode 3 and cathode 1 so that the loop 5 and the rod 2 do riot become unduly heated; If the tube is operated for some time, cathode 1 becomes heated, thereby reducing the density of the gas in its irnmediate vicinity and lowering the breakclown potential of the main discharge path betweenoathode 1 and anode 3. When the.

cathode 1 has been operated for a suflicient length of time, the density of the gas in its immediatevicnity is reduced to substantially an equilibrium level and the breakdown voltage between cathode 1 and anode 3 is reduced to substantially the same as the breakdown voltage between loop 5 and rod 2 so that if the discharge is turned ol and on while the cathode 1 is hot, the breakdownwill occur between anode 3 and cathode 1 as easily as between loop 5 and rod 2. Because the density of gas in the region of the loop 5 and rod 2 remains constantthe breakdown voltage of the secondary discharge path stays almost constant and the breakdown voltage between anode 3 and cathode 1 falls to this level. It should be noted that if the secondary discharge remained on for very long, i. e. if the discharge did not almost immediately transfer to cathode 1 and anode 3, there would be local heating of elements defining the secondary discharge path, and a resultant local change in gas density similar to the change in the region of the primary discharge path.

If the loop 5 were too close to the cathode 1 so that it was in a region where the density becarne reduced, there would be a decrease in breakdown voltage as the elements warmed up. If the loop 5 were too far away from the cathode 1,-there would be a slght increase in the breakdown voltage as the elements started to warm up and then a decrease as the cathode 1 came up to regular operating temperature.

In order to gve a more complete description of an operating embodiment of the invention the following dimensions are listed. These dimensions, however, are not to be considered as limiting the invention in any way. The cathode 1 is made of molybdenum of a thickness of .25 mm., an internal width of .55 mm, a height of 16 mm. and a length of 3 mm. The cathode is supported by rod 2 which has a length of 10 mm. a width of .7 mm., and a thickness of .25 mm. The wire 4 has a thickness of .4 mm. and terminates in a point 3 of .05 mm. The diameter of the loop 5 is 2.8 mm. and this loop is located at a distance of about 6 mm. from When the tube is cold, discharge takes the closest pointon cathode 1 and about 5 mm. from the conductive rod2. The" bulb"8has avolumeof about 6 cm. and is filled wth neon at a pressure of 48 mm. The internal diameter of the bulbis 18. mm. Without the 100p5, but wthall therdimensions as"listd,the breakdown Voltage between anode 3 and cathode I is 186i 10volts but witlith loopsas shwn inthedrawings, the breakdown voltage becomes moreconstantand .is 180i4 volts betweenthehot and the cold stats, an improvement of more than 50% in the reduction of the breakdown voltage tolerance.

While this inventionhas:been described in connecton with aspecific embodiment;modificatonstherein maybe made within the" scope of the fdllowing claims.

Whatis claimed is:

1. An electric dscharge tubecomprisingan envelope, an ionizable medium withnsid envelope, cathode and anode electrodes positioned within said envelope to definea main dschargepaththerebetWeen, and means connected in parallel With said anodeand cathode electrodes to define a secoridary dischargepath through said ionizable medium, said means beingspaced from said anode and cathode=electrodes and positioned Where the density of said ionizable mediumremains substantially constant irrespective to the temperatureof the medium whereby the breakdown pote'ntial ofsaid secondarydischarge path is substantiallythe same as"the breakdownpotential of the main discharge path when said tube is hot and the discharge-which initiates insaid secondary path is thereby transferred to said main dischargepath.

-2. An electric discharge tube comprising an envelope, anionizable medium within said envelope,"cathode and anode electrodes positioned withn saidenvelope to define a main discharge path therebetween a first conductive member supporting the cathode, "asecond coriductive member spaced fromand supporting: said anode, said second conductive member havng an extension facing the first conductive member and defining with the second conductive member a secondary discharge path, said extension being positioned relative to said anode and cathode electrodes where the densty of the ionizable medium remains substantially constant rrespective of the temperature of the medium whereby the breakdown po tential of saidsecondarypath is substantally the same asthe breakdown. potential of the main dscharge path whensaid tube is hotand the discharge which initiates in said secondary path isthereby transferred to said main discharge path.

3. Anelectric discharge tube comprising an envelope, an ionizablemediumwithin said envelope, cathode and anode electrdes positoned within said envelope to definc a main dischargepath1therebetween, a first conductive member supporting the cathode, a second conductve member spaced from and supporting saidanode, a crcular looP-likeektension on saidsecond conductive memberfacingsad first"conductivemember and spaced therefronr thereby defining a secondary discharge path therebetween, saidloop-like extension beng positioned rclative to said anode and 'cathodeelectrodes where the density ofthe ionizable medium remains substantially constant rrespective of thetemperature of the medium whereby'thebreakdown-potential ofsaid secondary path is=substantillybesame-asthe breakdown potential of the main discharge path when said tube is hot and the discharge=which initiates in said secondary path is transferred to--said-main discharge path. 

